Download Notes- Types of Dominance

Notes: Types of Dominance
1. Simple Dominance:
One gene is dominant over the other.
The recessive gene is hidden and not expressed.
Example- tongue rolling
Rolling tongue (R) is dominant to unable to roll
tongue (r)
2. Incomplete Dominance:
Neither allele is dominant over the other.
The heterozygous offspring will be a blend of the
two homozygous parents.
Example- flower color in snapdragons
RR=red flowers
Rr=pink flowers
rr=white flowers
Example- hair texture in humans
HH=curly hair
Hh=wavy hair
hh=straight hair
3. Codominance:
Both alleles are fully expressed when in the
heterozygous form.
Example- chicken feathers
BB=only black feathers
BW=black and white feathers on the same chicken
WW=only white feathers
Example- Human Blood Types
In humans, the allele for type A blood (IA) and the
allele for type B blood (IB) are codominant. O (i) is
recessive to both A and B.
Phenotypes
Type A
Type B
Type AB
Type O
Genotypes
IA IA or IA i
IB IB or IB i
IA IB
ii